This invention relates to locating uranium ore bodies. More particularly, it relates to a method of analyzing host rocks for radiation induced changes which can indicate the location of uranium ore bodies. This invention especially relates to the tracking of the migration of uranium ore bodies through geologic time by detecting radiation induced changes in organic matter associated with sedimentary deposits.
The location of mineral ore deposits has been of concern to mankind for centuries. A variety of techniques has been developed to locate and analyze deposits of economically important mineral ores. In many instances the deposit itself has to be located before a particular exploration procedure can effectively be employed. Samples of an ore have been obtained by drilling into the earth and removing a core sample for physical and chemical analysis. Geologging, electric logging and ultrasonic logging have been used for years in locating oil, natural gas and coal. More recently, gamma ray and neutron logging have proven successful in oil, gas and coal exploration. These procedures have also been employed with varying degrees of success in locating metal ore deposits.
Exploration techniques which can be successfully employed in the field without the requirement of collecting samples for later laboratory analysis are particularly preferred. One such procedure is described in South Africa patent application no. 80-3732 of Scintrex Limited which relates to a method for the detection of certain minerals of uranium, zinc, lead and other metals using photoluminescence. This method may be employed in the field and selectively rejects the fluorescent response of the abundant photoluminescent rocks and substances which occur at the surface of the earth while detecting the fluorescent response of a mineral of economic significance having a lifetime of photoluminescence between 1 and 500 microseconds through consideration of their differences in photoluminescent lifetimes.
Uranium ore deposits, because of their radioactive nature, may be easier to locate than other metal ores. However, one still must be in close proximity to a uranium ore deposit before detecting its radioactivity. Low grade deposits of uranium ore are widely distributed throughout the world and many have been found since some countries are willing to pay the cost of production from these deposits. On the other hand, higher-grade deposits are far less plentiful but some have been located. Those in the United States, Canada, France, and South Africa are among the principal ones which supply uranium ore to the free world. Locating high grade deposits of uranium ore which can be commercially developed remains an economically attractive venture.
Many sedimentary uranium ore bodies are continually mobilized, through geologic time, by ground waters moving through the sedimentary formation. As the ground waters move through the sediment, the ore body is gradually moved downstream by a process of solubilization and reprecipitation. Sometime in the geologic past, of course, these uranium ore bodies were located upstream from their present day location.
Because uranium minerals are radioactive, they produce radiation induced changes in sediments that contain them. As a uranium ore body is mobilized through a sediment, the host rocks are exposed to the radiation in the vicinity of the ore body. But while the ore body is moved downstream through the sedimentary strata, most other components of the host rock (e.g., sand grains, insoluble organic matter, etc.) are not. As a result, the mobilized ore body leaves a radiation induced signature or trail of its past positions.
Examination of likely host rocks for radiation induced changes can guide the explorationist in finding uranium ore bodies. If a radiation signature is observed in a sediment, but no uranium, the ore body will be found downstream. If there is no radiation signature, either the ore body is upstream, or there is no ore body in that part of the sediment.
It is an object of this invention to provide a method for finding uranium ore bodies.
It is another object of this invention to provide a method for analyzing host rocks to detect radiation induced changes in the rocks which have been caused by uranium ore deposits.
It is further object of this invention to detect uranium ore deposits by an indirect procedure.
The achievement of these and other objects will be apparent from the following description of the subject invention.